The invention is situated in the field of materials-handling technology and relates to a conveying method and to a conveying system for conveying piece goods including changeover between serial and parallel conveyance.
In the following, piece goods shall be understood to be a large number of objects that are conveyed either individually or in small groups in defined positions and, if so required, are processed and/or buffered. The piece goods are identical or at least so similar to one another that they all are conveyed, held during conveyance, and processed using the same means.
Piece goods are conveyed to processing stations and, after being processed, are conveyed away from processing stations. Processing means for processing piece goods are either essentially stationary, so that the objects are stopped for being processed, or else move along with the conveyed objects such that processing during continuous conveyance is possible.
For increasing throughput of such piece goods processing, rows of identical processing means are installed for simultaneous processing a plurality of objects (processing parallel in time).
Such a row of processing means operated simultaneously can be arranged in parallel to a conveying track, on which conveying track the objects are conveyed in series, i.e., in essence individually one after the other. Operation of such an arrangement takes place in processing cycles, in each of which one group of objects is processed, and conveying cycles alternating with processing cycles, in which the objects processed in the preceding processing cycle are conveyed away from the processing area and objects to be processed are conveyed into the processing area. For processing using a row of processing means arranged in parallel to the conveying track, the objects are conveyed in series only. In such processing, the length of the processing cycles is dependent on the processing process, the length of the conveying cycles on the number of objects to be processed simultaneously. Parallel processing in connection with serial conveyance is, for example, customary, if the piece goods are conveyed by a conveyor chain equipped with equidistant holding means for holding the objects.
If objects to be processed temporally parallel are also conveyed in parallel (locally parallel), i.e., along different conveying tracks running substantially in parallel, the row of processing means operated parallel in time is arranged transverse to the conveying direction. In this case the conveying cycles alternating with the processing cycles become shorter in comparison with the method mentioned above and, accordingly, the throughput becomes correspondingly higher. However, a more elaborate conveying device has to be provided in addition to means for changing the conveying method (serial/parallel), if parallel conveyance is advantageous in specific zones only, in other zones serial conveyance being desirable. Such changing means are, for example, switch points for branching and for joining together conveying paths, with the help of which a serial stream of conveyed objects is split-up into parallel part streams or a plurality of parallel part streams is joined to form one serial conveying stream. For such conveying methods, conveyor chains with holding means can only be utilised, if the objects are correspondingly transferred at the switch points. More simply, the objects are conveyed by suitable guide means (e.g. conveyor belts) and are accurately positioned in processing stations, in most cases by being taken over by correspondingly designed holding means to be held in a predefined position for being processed.
The changeover between serial conveyance and parallel conveyance with the help of branching and joining switch points can be implemented also in conveying systems with rail-like guide means and with a plurality of conveying means being independent of one another, being equipped for conveying in held manner one object each or a small group of objects, and being individually movable along the rail-like guide means. In conveying systems of this kind, the products do not need to be transferred at switch points. However, elaborate switch points and parallel rail stretches, both using a lot of space are still needed for the changeover between serial and parallel conveyance.
Further known methods for changes between serial and parallel conveyance use holding means, each equipped for holding a row of objects and being conveyed with the held object row oriented either parallel to the conveying direction (serial conveyance) or substantially perpendicular to the conveying direction (parallel conveyance). Either, such holding means are mounted rotatably on suitable conveying means or different kinds of rails are provided for serial conveyance and for parallel conveyance (e.g. described in DE-19717352). Using such holding means, no great effort is needed for the change between parallel conveyance and serial conveyance. However, additional means are needed for picking single objects out of the rows for individual handling.
It is an object of the invention to create a method for conveying piece goods using a conveying system comprising rail-like guide means and conveying means being movable along the rail-like guide means independently of one another and being equipped for holding individual objects or small groups of objects. The method is adaptable for any desired changeover between serial and parallel conveyance. In particular, the method enables parallel conveyance with different numbers of objects being conveyed in parallel, reduces object transfers as far as possible and nonetheless is simple, utilisable as universally as possible and is applicable with as few and as simple as possible means. Furthermore, it is the object of the invention to create a conveying system for implementing the method.
In a conveying system with rail-like guide means and with conveying means being independently movable along the rail-like guide means, changeover from serial to parallel conveyance is implemented according to the inventive method by bringing a displaceable rail element into a first position, in which it is in connection with a further, essentially stationary rail element, by serially moving a plurality of conveying means from the stationary rail element to the displaceable rail element, by blocking the plurality of conveying means on the displaceable rail element, and by displacing the displaceable rail element together with the conveying means blocked on it essentially transverse to the conveying direction of the serial conveyance, i.e. in essence transverse to its length, which for the conveying means blocked on the rail element is equivalent to parallel conveyance.
For a change from such parallel conveyance back to serial conveyance, the displaceable rail element is brought (again essentially transverse to its length) into a position, in which it once again connects with an essentially stationary rail element, the conveying means are unblocked on the displaceable rail element and are serially conveyed away from the displaceable rail to the stationary rail element.
The conveying means, which according to the inventive method are conveyed partly serially and partly in parallel, are, for example, each equipped with a holding means for holding one object. During changeover from serial to parallel conveyance they carry objects to be processed. During parallel conveyance the objects are processed and the conveying means carry processed objects at the changeover from parallel to serial conveyance. Temporary changeover from serial conveyance to parallel conveyance according to the invention can also be utilised for parallel loading or unloading of conveying means or for buffering or intermediate storage of conveying means or objects respectively.
Important advantages of the conveying system according to the invention include the features that within the same conveying system different zones with parallel conveyance with different numbers of parallel conveying routes can be implemented and that the conveying means are completely independent of one another in zones with serial conveyance.
If the conveying means are blocked in predefined positions on the displaceable rail element, then the objects are maintained in defined positions for a processing operation during parallel conveyance and do not have to be transferred to holding elements of the processing station. A simple manner for blocking the conveying means on the displaceable rail element consists of conveying the maximum possible number of conveying means onto the rail element and closing-off both ends of the rail element. The blocked conveying means keep each other in defined positions along the displaceable rail element.
In a preferred embodiment of the invention, a plurality of identical displaceable rail elements are used for parallel conveyance. One after the other of these displaceable elements are brought into the first position, loaded with conveying means, and then displaced one behind the other and essentially transverse to the direction of serial conveyance. According to a further, advantageous embodiment of the invention, the displaceable rail elements are displaced along a closed in itself displacement path and the first position is the same as the second one, i.e., a position, in which on both sides of the displaceable rail element a stationary rail element is adjoining. In an embodiment of this type, a group of conveying means on a displaceable rail element is exchanged whereby the group positioned on the displaceable rail element is pushed off by a new group.
For the named, preferred embodiments of the invention it is particularly advantageous to use conveying systems with rails and conveying means designed such that conveyance along the rails is possible in every position of the conveying means relative to the rail. A conveying system of this kind and parts of it are described, for example, in the publications EP-0387318 (or U.S. Pat. No. 5,074,678), EP-0870934 or WO-98/23509 of the same applicant.
The conveying system for the implementation of the method in accordance with the invention comprises rail-like guide means and conveying means movable along the rail-like guide means independently of one another and equipped for held conveyance of individual objects or of small groups of objects, wherein at least one rail element is displaceable essentially transverse to its length into a position, in which it connects with an essentially stationary rail element, and out of this position. Advantageously, the conveying system comprises a plurality of displaceable rail elements, which are displaceable one after the other along a displacement path closed in itself, wherein in at least one of the displacement positions a stationary rail element joins with the displaceable rail element.
A means for the displacement of a plurality of rail elements on a closed in itself displacement path is, for example, a rail arrangement driven to rotate around a rotational axis, in which a plurality of displaceable rail elements is arranged parallel to the rotation axis and at equal spacings between each other. This rail arrangement is integrated in the conveying system such that its rotation axis is aligned parallel to the direction of serial conveyance.